Sleep deprivation (SD) contributes to cognitive impairment. Astrocytic cholesterol biosynthesis is crucial for brain cholesterol homeostasis and cognitive function. However, the underlying mechanism of astrocytic cholesterol metabolism in SD-induced cognitive impairment has not been fully explored. Trimethylamine N-oxide (TMAO), a product of liver flavin-containing monooxygenase-3 (FMO3), has been shown to be increased in the urine of sleep-deprived humans and implicated with peripheral cholesterol metabolism. Nevertheless, how TMAO affects brain cholesterol metabolism remains unclear. In our study, increased FMO3 and brain TMAO levels were observed in the SD mice, and elevated levels of TMAO were confirmed to lead to SD-induced cognitive dysfunction. In addition, we found that the expression of sterol regulatory element-binding protein 2 (SREBP2) is decreased in the brain of SD mice, resulting in the reduction in brain cholesterol content, which in turn causes synaptic damage. Moreover, we demonstrated that TMAO inhibits the expression of SREBP2. In contrast, FMO3 inhibitor 3,3′-diindolylmethane (DIM) alleviates SD-induced cognitive impairment by targeting the liver–brain axis. In conclusion, our study revealed that the TMAO pathway is involved in memory impairment in SD mice through deregulating astrocytic cholesterol metabolism.

Cognitive dysfunction has become the second leading cause of death among the diabetic patients. In pre-diabetic stage, blood-brain barrier (BBB) injury occurs and induced the microvascular complications of diabetes, especially, diabetes-associated cognitive dysfunction (DACD). Endothelial cells are the major component of BBB, on which the increased expression of CD40 could mediate BBB dysfunction in diabetics. Since platelets play an important role in regulating endothelial cell barrier function and over 95 % of the circulating soluble CD40 ligand (sCD40L) is derived from activated platelets, we speculated that the release of CD40L from activated platelets induced by diabetes was the key mechanism that aggravated BBB injury and leaded to DACD. We performed inhibition of platelet activation on diabetic and non-diabetic mice, with or without cilostazol treatment, and then compared cognitive function, platelet activation, BBB structure and permeability. In vitro, mouse brain microvascular endothelial cell line (b.End3) were exposed to CD40L for 24 h at 5.5 mM or 30 mM glucose media after silencing CD40 and HIF1α or not to investigate the effects of CD40 on BBB disruption and the underlying molecular pathways. Inhibition of platelet activation improved cognitive behaviors in diabetic mice, accompanied with reduced BBB permeability, increased tight junction proteins, balanced Aβ transporters, as well as attenuated Aβ deposition and hippocampal neurons damage. In vitro, CD40L increased HIF1α, diminished tight junction proteins and dysregulated Aβ transporters in b.End3 cells, which could be restored by CD40 siRNA and HIF1α siRNA. Hence, inhibition of platelet activation ameliorates DACD via alleviating BBB injury, which involving the regulation of CD40L-CD40-HIF1α signaling pathway. Our study may demonstrate a potential therapeutic target for the treatment of DACD.

Mitochondrial dysfunction and neuronal impairment are hallmark features of Diabetes-Associated Cognitive Dysfunction (DACD), mitochondrial transplantation is also a therapeutic intervention for DACD. However, the precise mechanism underlying its therapeutic effects are not fully elucidated. Given that imbalances in copper homeostasis and cuproptosis are associated with various neurodegenerative disorders and diabetic myocardial damage, we hypothesize a role for cuproptosis in the pathogenesis of DACD. We further propose that therapeutic peripheral mitochondrial transplantation may ameliorate DACD by reducing processes of cuproptosis. In this research, the study delved into the expression levels of cuproptosis-associated proteins FDX1, LIAS, and DLAT, as well as the copper content in both type 2 diabetes mellitus (T2DM) mice and primary neuronal cells exposed to high glucose and palmitic acid (HG/Pal). Furthermore, the cognitive capabilities of the mice were evaluated using a series of behavioral tests. The findings revealed that in primary neurons exposed to HG/Pal, the expression of copper levels was elevated, and the levels of FDX1, LIAS, and DLAT were reduced. Post-transplantation of platelet-derived mitochondria (Mito-Plt), a significant reversal of these biomarkers was noted, coincident with an improvement in cognitive deficits in T2DM mice. Significantly, the cuproptosis agonist elesclomol (ES) aggravated these alterations. In summary, the findings collectively suggest a causal connection between DACD and the development of cuproptosis in neurons. The use of exogenous Mito-Plt presents a promising therapeutic approach, capable of rescuing neurons from cuproptosis and thereby potentially alleviating DACD.